JP2014162103A - Method for manufacturing electroconductive roller, electroconductive roller, and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electroconductive roller resistant to occurrences of image defects, etc. by inhibiting excessive reductions of foam cell diameters in the vicinity of the outer surface thereof; the electroconductive roller manufactured by the manufacturing method, and an image forming device with which the electroconductive roller is integrated.SOLUTION: The provided manufacturing method includes a step of forming a cylindrical foam 1 by continuously extrusion-molding, as a cylindrical object, a rubber composition from the nozzle of an extruder head under the condition of the head pressure being 25 MPa or below and then cutting, at a specified length, and heating, foaming, and crosslinking the molded cylinder within a vulcanizer. An electroconductive roller 4 possesses the cylindrical foam 1 manufactured past the prescribed step. The electroconductive roller is integrated with the image forming device as a charging roller, development roller, transfer roller, etc.

Description

  The present invention relates to a method for manufacturing a conductive roller, a conductive roller manufactured by the manufacturing method, and an image forming apparatus incorporating the conductive roller.

For example, in an image forming apparatus using electrophotography such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine, or a complex machine of these, paper (plastic film such as an OHP film) is roughly processed through the following steps. An image is formed on the surface of the same.
First, the surface of the photoconductive photoconductor is exposed in a uniformly charged state, and an electrostatic latent image corresponding to the formed image is formed on the surface (charging step → exposure step).

Next, the toner, which is minute colored particles, is brought into contact with the surface of the photoconductor in a state of being charged to a predetermined potential. Then, the toner is selectively attached to the surface of the photoconductor according to the potential pattern of the electrostatic latent image, and the electrostatic latent image is developed into a toner image (development process).
Next, the toner image is transferred to the surface of the paper (transfer process) and further fixed (fixing process), whereby an image is formed on the surface of the paper.

In the transfer step, the toner image formed on the surface of the photoconductor is not only directly transferred to the surface of the paper, but also transferred to the surface of the image carrier (primary transfer step) and then transferred to the surface of the paper. In some cases, retransfer is performed (secondary transfer process).
Further, a series of image formation is completed by removing the toner remaining on the surface of the photoreceptor after the transfer (cleaning process).

The charging process, the developing process, the transferring process, and the cleaning process of the photosensitive member among the above-described processes are performed from a foamed rubber tubular body (cylindrical foamed body) that is provided with conductivity according to each application. Thus, a conductive roller in contact with the surface of the photoreceptor is widely used.
The conductive roller is formed by continuously extruding a rubber composition having, for example, conductivity, crosslinkability, and foamability through a head of an extruder into a cylindrical shape, and then cutting the rubber composition to a predetermined length. In general, after heating and foaming and crosslinking in a tube, a cored bar is inserted and fixed in the cylinder (Patent Documents 1, 2, etc.).

JP 2004-262110 A JP 2006-231617 A

  However, the conventional conductive roller manufactured by the manufacturing method according to claims 1 and 2 is a foamed cell in which the diameter of the foamed cell (foamed cell diameter) in the vicinity of the outer surface thereof is radially inward. As a result, the contact area of the outer surface with respect to the surface of the photosensitive member is greatly deviated from a predetermined value, and as a result, there is a problem that an image defect is likely to occur in a formed image. .

  An object of the present invention is to provide a manufacturing method for manufacturing a conductive roller which suppresses the foam cell diameter in the vicinity of the outer surface from becoming too small and hardly causes image defects, and the conductive roller manufactured by the manufacturing method. And an image forming apparatus incorporating the conductive roller.

In the present invention, a rubber composition having electrical conductivity, crosslinkability, and foamability is continuously extruded into a cylindrical shape through a head of an extruder under a head pressure of 25 MPa or less, and then cut into a predetermined length. Then, it is a method for producing a conductive roller, comprising a step of heating in a vulcanizing can and foaming and crosslinking to form a cylindrical foam.
Further, the present invention is a conductive roller manufactured by the manufacturing method of the present invention.

According to the inventor's study, in the conventional production methods described in Patent Documents 1 and 2, etc., it is common to extrude the rubber composition with the head pressure during extrusion set to a high pressure exceeding 25 MPa. It is.
However, the higher the head pressure, the higher the temperature near the outer surface of the extruded foam and the cylindrical body before crosslinking. The temperature rise includes a temperature rise due to friction between the head die and the cylindrical body in the middle of extrusion molding.

  As the temperature near the outer surface becomes higher than the inside and the temperature difference between the inside and outside becomes larger, the timing of foaming and crosslinking in the next step deviates from the design value especially near the outer surface, and after foaming and crosslinking In the cylindrical foam, the diameter of the foam cell in the vicinity of the outer surface is smaller than the diameter of the foam cell inside in the radial direction, and the photoconductive body of the conductive roller manufactured using the cylindrical foam. As a result, the contact area with respect to the surface greatly deviates from a predetermined value, so that an image defect is likely to occur in the formed image.

On the other hand, according to the present invention, as described above, by setting the head pressure during extrusion molding to 25 MPa or less, it is possible to increase the temperature near the outer surface of the extruded foam and the cylindrical body before crosslinking. Thus, the temperature difference between the vicinity of the outer surface and the radially inner side can be reduced, and the timing of foaming and crosslinking in the next step can be made substantially close to the design value for the entire cylindrical body.
Therefore, in the tubular foam after foaming and crosslinking, the foamed cell diameter in the vicinity of the outer surface is suppressed from becoming too smaller than the foamed cell diameter radially inward, and the tubular foam is used. The displacement of the contact area of the conductive roller manufactured in this manner with respect to the surface of the photosensitive member can be suppressed, and image defects associated with the displacement can be made difficult to occur.

In consideration of further improving this effect, the head pressure during the extrusion is preferably 20 MPa or less.
Also, if the outer surface of the foamed and cross-linked tubular foam is polished in the next step to remove a region with a small foam cell diameter in the vicinity of the outer surface, the occurrence of image defects can be further ensured. Can be prevented.

However, the radial polishing thickness of the outer surface is preferably 3 mm or less in consideration of the waste of material and the time required for polishing as much as possible to improve the productivity of the conductive roller.
The rubber composition includes at least a rubber component, a crosslinking agent component for crosslinking the rubber component, and a foaming agent component, and the foaming agent component is 1 part by mass or more per 100 parts by mass of the total rubber component. It is preferable to use only a foaming agent of 10 parts by mass or less, or a foaming agent of the above amount and 5 parts by mass or less of a foaming aid per 100 parts by mass of the total amount of the rubber.

  As a foaming agent component, excluding foaming aids that lower the foaming cell's decomposition temperature and reduce the cell diameter of the foamed cells, that is, without any foaming aids, it decomposes by heating to generate gas. Even if only the foaming agent to be used is used alone or the foaming aid is blended, the foamed cell diameter can be increased in the entire cylindrical foam by blending with the blending ratio limited to the above range. Can do.

In addition, by making the blending ratio of the foaming agent within the above range, the cylindrical body can be foamed well, the cross-sectional shape of the outer surface and the inner surface of the cylindrical foam after foaming and crosslinking is made into a clean circle, and the inner diameter It is also possible to produce a conductive roller having a uniform hardness and a small non-uniformity in electrical conductivity by making the dimensions of the foam as uniform as possible and further making the distribution of the foamed cells as uniform as possible.
Therefore, the occurrence of image defects can be prevented more reliably.

The present invention is an image forming apparatus in which the conductive roller of the present invention is incorporated.
According to the image forming apparatus of the present invention, the built-in conductive roller of the present invention can be brought into contact with the surface of the photoconductor with a predetermined contact area, so that an image defect based on a deviation from the predetermined value of the contact area occurs. Can be difficult.

  According to the present invention, a manufacturing method for manufacturing a conductive roller that suppresses the foam cell diameter in the vicinity of the outer surface from becoming too small and hardly causes image defects, and the conductive roller manufactured by the manufacturing method. In addition, an image forming apparatus incorporating the conductive roller can be provided.

It is a perspective view which shows an example of the electroconductive roller of this invention manufactured by the manufacturing method of this invention. It is sectional drawing explaining the measuring method of the foam cell diameter in the electroconductive roller manufactured by the Example of this invention and the comparative example.

<< Conductive Roller Manufacturing Method and Conductive Roller >>
FIG. 1 is a perspective view showing an example of the conductive roller of the present invention manufactured by the manufacturing method of the present invention.
In the production method of the present invention, a rubber composition formed by kneading ingredients such as a rubber component and a foaming agent in a predetermined ratio to form a ribbon or the like is first supplied to the extruder while continuously feeding the extruder. By operating, the long cylindrical body is continuously extruded through the die of the head.

Next, the extruded cylindrical body is cut into a predetermined length, heated in a vulcanizing can, foamed, and crosslinked to form a cylindrical foam.
Next, referring to FIG. 1, the conductive roller 4 is manufactured by inserting and fixing the cored bar 3 into the through hole 2 of the formed cylindrical foam 1 and further performing secondary crosslinking as necessary. .
In the present invention, among the above steps, the head pressure when the rubber composition is extruded by an extruder is set to 25 MPa or less.

As a result, as described above, the temperature increase between the outer surface and the radially inner portion is reduced by suppressing the temperature increase near the outer surface of the extruded cylindrical body before crosslinking. The timing of foaming and cross-linking in the next process can be brought close to the design value for the entire cylindrical body.
Therefore, the foamed cell diameter in the vicinity of the outer surface 5 becomes too smaller than the foamed cell diameter radially inward in the tubular foam 1 after foaming and crosslinking, and accordingly the conductive roller 4 It is possible to suppress the occurrence of image defects by suppressing the contact area with respect to the surface of the photoreceptor from shifting.

In consideration of further improving this effect, the head pressure during the extrusion is preferably 20 MPa or less.
The lower limit value of the head pressure is not particularly limited, but is preferably 5 MPa or more, particularly 10 MPa or more. If the head pressure is less than the above range, the extrusion speed becomes low, the time during which the rubber composition stays in the extruder 3 becomes long, and there is a possibility that the rubber is burnt.

In order to adjust the head pressure, for example, in an extruder, a hopper for supplying a rubber composition, a front part (hopper side) of a cylinder for melting the rubber composition supplied to the hopper, and a rear part The temperature of each part of the head (head side) and the head may be adjusted.
Specifically, the higher the overall temperature, the lower the melt viscosity of the rubber composition, so that the head pressure can be reduced. Conversely, the lower the overall temperature, the higher the melt viscosity, the higher the head. The pressure can be increased.

Further, the head pressure can be finely adjusted by changing the type and combination of rubber components constituting the rubber composition or changing the amount of the filler.
Specifically, the more the rubber component having a low melt viscosity at the same temperature is blended, and the smaller the amount of the filler, the lower the melt viscosity of the rubber composition, so the head pressure is lowered. Conversely, the more the rubber component having a high melt viscosity at the same temperature is blended, the more the amount of the filler is increased, the higher the melt viscosity of the rubber composition increases. Can be made.

In the present invention, the outer surface 5 of the tubular foam 1 is polished in an arbitrary process until the conductive roller 4 is completed using the foamed and crosslinked tubular foam 1. Is preferred.
Thereby, it is possible to more reliably prevent the occurrence of image defects.
However, the radial polishing thickness of the outer surface 5 is preferably 3 mm or less in consideration of waste of materials and the improvement of the productivity of the conductive roller 4 by reducing the time required for polishing as much as possible. .

The timing of polishing can be set arbitrarily, but the outer surface 5 of the cylindrical foam 1 in the state of FIG. 1 cut into a predetermined length and inserted through the core metal 3 is fixed around the core metal 3. Polishing while rotating is preferable in terms of improving workability and suppressing the flare of the outer surface 5.
The core metal 3 is integrally formed of a metal such as aluminum, an aluminum alloy, or stainless steel.

The core metal 3 having an outer diameter larger than the inner diameter of the through hole 2 is press-fitted into the through hole 2 at the center of the cylindrical foam 1 so that the both are electrically joined and mechanically fixed. Thus, the conductive roller 4 is configured.
Note that, for example, the two may be electrically joined and mechanically fixed with an adhesive having conductivity.

The conductive roller 4 can be used by being incorporated in an image forming apparatus using electrophotography, for example, as a charging roller, a developing roller, or a transfer roller.
The rubber composition used as the basis of the cylindrical foam 1 has foamability and crosslinkability that foam and crosslink when heated in the vulcanizing can, and is used for the conductive roller 4 and the like. Any rubber composition having any conductivity can be used.

In particular, a rubber composition imparted with ionic conductivity using an ionic conductive rubber also serving as a rubber component is preferable as the conductivity imparting agent.
<Rubber composition>
<Ion conductive rubber>
As the rubber component, it is preferable to use the ion conductive rubber and the crosslinkable rubber in combination.

  Among these, as ionic conductive rubber, epichlorohydrin homopolymer, epichlorohydrin-ethylene oxide binary copolymer (ECO), epichlorohydrin-propylene oxide binary copolymer, epichlorohydrin-allyl glycidyl ether binary copolymer, epichlorohydrin- 1 type of ethylene oxide-allyl glycidyl ether terpolymer (GECO), epichlorohydrin-propylene oxide-allyl glycidyl ether terpolymer, and epichlorohydrin-ethylene oxide-propylene oxide-allyl glycidyl ether quaternary copolymer Or 2 or more types are mentioned.

As the epichlorohydrin rubber, among the above examples, a copolymer containing ethylene oxide, particularly ECO and / or GECO is preferable.
In both copolymers, the ethylene oxide content is preferably 30 mol% or more, particularly preferably 50 mol% or more, and preferably 80 mol% or less.
Ethylene oxide serves to lower the roller resistance value of the entire conductive roller 4. However, if the ethylene oxide content is less than the above range, such a function cannot be obtained sufficiently, and the roller resistance value of the conductive roller 4 may not be sufficiently reduced.

On the other hand, when the ethylene oxide content exceeds the above range, crystallization of ethylene oxide occurs and the segmental movement of the molecular chain is hindered, so that the roller resistance value of the conductive roller 4 tends to increase. In addition, the hardness of the foamed and crosslinked tubular foam 1 may be increased, or the viscosity of the rubber composition before crosslinking may be increased when heated and melted.
The epichlorohydrin content in ECO is the remaining amount of the ethylene oxide content. That is, the epichlorohydrin content is preferably 20 mol% or more, preferably 70 mol% or less, and particularly preferably 50 mol% or less.

Further, the allylic glycidyl ether content in GECO is preferably 0.5 mol% or more, particularly preferably 2 mol% or more, more preferably 10 mol% or less, and particularly preferably 5 mol% or less.
The allyl glycidyl ether itself functions to secure a free volume as a side chain, thereby suppressing the crystallization of ethylene oxide and reducing the roller resistance value of the conductive roller 4. However, when the allyl glycidyl ether content is less than the above range, such a function cannot be obtained, so that the roller resistance value of the conductive roller 4 may not be sufficiently reduced.

  On the other hand, allyl glycidyl ether functions as a crosslinking point at the time of GECO crosslinking, so when the allyl glycidyl ether content exceeds the above range, the GECO crosslinking density becomes high, and segment movement of molecular chains is hindered. On the contrary, the roller resistance value of the conductive roller 4 tends to increase. Moreover, there exists a possibility that the tensile strength of the cylindrical foam 1, fatigue characteristics, bending resistance, etc. may fall.

The epichlorohydrin content in GECO is the remaining amount of the ethylene oxide content and the allyl glycidyl ether content. That is, the epichlorohydrin content is preferably 10 mol% or more, particularly 19.5 mol% or more, preferably 69.5 mol% or less, particularly preferably 60 mol% or less.
As GECO, in addition to a copolymer in the narrow sense obtained by copolymerizing the above three types of monomers, a modified product obtained by modifying epichlorohydrin-ethylene oxide copolymer (ECO) with allyl glycidyl ether is also known. Any GECO can be used in the present invention.

The blending ratio of epichlorohydrin rubber is preferably 5 parts by mass or more, particularly 10 parts by mass or more, and preferably 40 parts by mass or less, particularly 30 parts by mass or less, in 100 parts by mass of the total amount of rubber.
If the blending ratio is less than the above range, the tubular foam 1 may not be provided with good ionic conductivity.

On the other hand, when the above range is exceeded, the blending ratio of the crosslinkable rubber is relatively decreased, and there is a possibility that the effect obtained by blending various crosslinkable rubbers described later cannot be sufficiently obtained.
<Crosslinkable rubber>
Examples of the crosslinkable rubber include styrene butadiene rubber (SBR) and / or acrylonitrile butadiene rubber (NBR). These rubbers have not only good crosslinkability but also function to impart good rubber elasticity and flexibility to the foamed and foamed cylindrical foam 1.

Further, when ethylene propylene diene rubber (EPDM) is further blended as the crosslinkable rubber, the resistance of the cylindrical foam 1 to ozone generated in the image forming apparatus can be improved.
(SBR, NBR)
Of these, as the SBR, any of various SBRs synthesized by copolymerizing styrene and 1,3-butadiene by various polymerization methods such as an emulsion polymerization method and a solution polymerization method can be used. In addition, as SBR, there are an oil-extended type in which flexibility is adjusted by adding an extending oil and a non-oil-extended type in which flexibility is not added, either of which can be used.

Furthermore, as the SBR, any of SBR of high styrene type, medium styrene type, and low styrene type classified by styrene content can be used. Various physical properties of the cylindrical foam 1 can be adjusted by changing the styrene content and the degree of crosslinking.
One or more of these SBRs can be used.
As NBR, any of low nitrile NBR, medium nitrile NBR, medium high nitrile NBR, high nitrile NBR, and extremely high nitrile NBR classified by acrylonitrile content can be used. One or more of these NBRs can be used.

Furthermore, SBR and NBR can be used in combination.
The blending ratio of SBR and / or NBR is preferably 40 parts by mass or more, particularly 60 parts by mass or more, and particularly 90 parts by mass or less, particularly 80 parts by mass or less, in 100 parts by mass of the total amount of rubber. preferable.
When the blending ratio is less than the above range, by using SBR and / or NBR, the effect of imparting good crosslinkability to the rubber composition, the foaming, and the tubular foamed body 1 after crosslinking are described above. There is a possibility that the effect of imparting good rubber elasticity and flexibility cannot be obtained sufficiently.

On the other hand, when the above range is exceeded, there is a possibility that the blending ratio of EPDM is relatively small and the tubular foam 1 cannot be given good ozone resistance. In addition, the proportion of the epichlorohydrin rubber may be relatively reduced, and the tubular foam 1 may not be provided with good ionic conductivity.
In addition, the said mixture ratio is a mixture ratio of SBR itself as solid content contained in the oil-extended type SBR when using an oil-extended type SBR. Moreover, when using SBR and NBR together, it is the total blending ratio.
(EPDM)
As EPDM, any of various EPDMs in which a double bond is introduced into the main chain by adding a small amount of a third component (diene component) to ethylene and propylene can be used. As the EPDM, various products are provided depending on the kind and amount of the third component. Representative examples of the third component include ethylidene norbornene (ENB), 1,4-hexadiene (1,4-HD), dicyclopentadiene (DCP), and the like. A Ziegler catalyst is generally used as the polymerization catalyst.

The blending ratio of EPDM is preferably 5 parts by mass or more, more preferably 40 parts by mass or less, and particularly preferably 20 parts by mass or less, in 100 parts by mass of the total rubber content.
When the blending ratio is less than the above range, there is a possibility that good ozone resistance cannot be imparted to the tubular foam 1.
On the other hand, if the above range is exceeded, the blending ratio of SBR and / or NBR is relatively reduced, and by blending these rubbers, the effect of imparting good crosslinkability to the rubber composition, There is a possibility that the effect of imparting good rubber elasticity and flexibility to the foamed and crosslinked tubular foam 1 may not be sufficiently obtained. In addition, the proportion of the epichlorohydrin rubber may be relatively reduced, and the tubular foam 1 may not be provided with good ionic conductivity.

(Other rubber)
As a rubber component, polar resistance such as chloroprene rubber (CR), butadiene rubber (BR), and acrylic rubber (ACM) can be further blended to finely adjust the roller resistance value of the conductive roller 4.
<Foaming agent component>
As a foaming agent component, only a foaming agent that decomposes by heating and generates a gas to foam the rubber composition can be used at a ratio of 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the total amount of rubber. It is preferable to use the foaming agent of the above amount and the foaming aid of 5 parts by mass or less per 100 parts by mass of the total amount of the rubber.

  As a foaming agent component, excluding foaming aids that lower the foaming cell's decomposition temperature and reduce the cell diameter of the foamed cells, that is, without any foaming aids, it decomposes by heating to generate gas. Even if only the foaming agent to be used is used alone or the foaming aid is blended, the foamed cell diameter can be increased in the entire cylindrical foam by blending with the blending ratio limited to the above range. Can do.

In addition, by making the blending ratio of the foaming agent within the above range, the cylindrical body can be foamed well, and the cross-sectional shape of the outer surface 5 and the inner surface of the cylindrical foam 1 after foaming and crosslinking is made into a clean circle, In addition, it is possible to produce a conductive roller having uniform inner diameter dimensions as much as possible and further making the distribution of the foamed cells as uniform as possible so that the hardness and the conductivity unevenness are small.
Therefore, the occurrence of image defects can be prevented more reliably.

Examples of the foaming agent include azodicarbonamide (H ₂ NOCN = NCONH ₂ , ADCA), 4,4′-oxybis (benzenesulfonylhydrazide) (OBSH), N, N-dinitrosopentamethylenetetramine (DPT), and the like. 1 type or 2 types or more are mentioned.
Moreover, urea is mentioned as a foaming adjuvant.

<Crosslinking agent component>
In the rubber composition, a crosslinking agent component for crosslinking the rubber component is blended. Examples of the crosslinking agent component include a crosslinking agent and an accelerator.
Among these, examples of the crosslinking agent include one or more of sulfur-based crosslinking agents, thiourea-based crosslinking agents, triazine derivative-based crosslinking agents, peroxide-based crosslinking agents, various monomers, and the like. Of these, sulfur-based crosslinking agents are preferred.

Examples of sulfur-based crosslinking agents include powdered sulfur and organic sulfur-containing compounds. Among these, examples of the organic sulfur-containing compound include tetramethylthiuram disulfide and N, N-dithiobismorpholine. In particular, sulfur such as powdered sulfur is preferred.
The blending ratio of sulfur is preferably 0.2 parts by mass or more, particularly 1 part by mass or more, preferably 5 parts by mass or less, particularly 3 parts by mass or less, per 100 parts by mass of the total amount of rubber.

When the blending ratio is less than the above range, the crosslinking rate of the rubber composition as a whole becomes slow, and the time required for crosslinking becomes long, and the productivity of the conductive roller 4 may be lowered. Moreover, when exceeding the said range, there exists a possibility that the compression set of the cylindrical foam 1 after foaming and bridge | crosslinking may become large, or excessive sulfur may bloom on the outer surface 5 of the cylindrical foam 1. .
Examples of the accelerator include inorganic accelerators such as slaked lime, magnesia (MgO), and resurge (PbO), and one or more organic accelerators.

  Examples of the organic accelerator include guanidine accelerators such as di-o-tolylguanidine, 1,3-diphenylguanidine, 1-o-tolylbiguanide, dicatechol borate di-o-tolylguanidine salt; 2-mercapto Thiazole accelerators such as benzothiazole and di-2-benzothiazyl disulfide; sulfenamide accelerators such as N-cyclohexyl-2-benzothiazylsulfenamide; tetrametherthiuram monosulfide, tetramethylthiuram One type or two or more types of thiuram accelerators such as disulfide, tetraethylthiuram disulfide, and dipentamethylene thiuram tetrasulfide;

As the accelerator, one or more kinds of optimum accelerators may be selected from the various accelerators according to the type of the crosslinking agent to be combined. For example, when sulfur is used as a crosslinking agent, it is preferable to select and use a thiuram accelerator and / or a thiazole accelerator as an accelerator.
Moreover, since the acceleration | stimulation mechanism of a crosslinking agent changes with kinds, it is preferable to use 2 or more types together. The blending ratio of the individual accelerators used in combination can be arbitrarily set, but it is preferably 0.1 parts by mass or more, particularly 0.5 parts by mass or more, preferably 8 parts by mass per 100 parts by mass of the total amount of rubber. Hereinafter, it is particularly preferably 5 parts by mass or less.

As the cross-linking agent component, an accelerator aid may be further blended.
Examples of the acceleration aid include one or more metal compounds such as zinc oxide; fatty acids such as stearic acid, oleic acid, and cottonseed fatty acid; and other conventionally known acceleration aids.
The blending ratio of the accelerator aid can be appropriately set according to the kind and combination of the rubber component, the kind and combination of the crosslinking agent and accelerator, and the like.

(Other)
You may mix | blend various additives with a rubber composition further as needed. Examples of the additive include acid acceptors, plastic components (plasticizers, processing aids, etc.), deterioration inhibitors, fillers, scorch inhibitors, ultraviolet absorbers, lubricants, pigments, antistatic agents, flame retardants, Examples thereof include a compatibilizer, a nucleating agent and a co-crosslinking agent.

Of these, the acid acceptor functions to prevent the chlorine-based gas generated from the epichlorohydrin rubber during the crosslinking of the rubber component from remaining in the cylindrical foam 1, thereby inhibiting cross-linking and contamination of the photoreceptor. .
As the acid acceptor, various substances that act as an acid acceptor can be used, but hydrotalcites or magsarat are preferable because of excellent dispersibility, and hydrotalcites are particularly preferable.

Further, when the hydrotalcite or the like is used in combination with magnesium oxide or potassium oxide, a higher acid receiving effect can be obtained, and contamination of the photoreceptor can be prevented more reliably.
The blending ratio of the acid acceptor is preferably 0.2 parts by mass or more, particularly 0.5 parts by mass or more, preferably 5 parts by mass or less, particularly 3 parts by mass or less, per 100 parts by mass of the total amount of rubber. preferable.
If the blending ratio is less than the above range, the above-described effect due to the inclusion of the acid acceptor may not be sufficiently obtained. Moreover, when exceeding the said range, there exists a possibility that the hardness of the cylindrical foam 1 after foaming and bridge | crosslinking may rise.

Examples of the plasticizer include various plasticizers such as dibutyl phthalate (DBP), dioctyl phthalate (DOP), and tricresyl phosphate, and various waxes such as polar wax. Examples of the processing aid include fatty acids such as stearic acid.
The blending ratio of these plastic components is preferably 5 parts by mass or less per 100 parts by mass of the total amount of rubber. For example, this is to prevent the photosensitive member from being contaminated when it is attached to the image forming apparatus or during operation. In view of this object, it is particularly preferable to use a polar wax as the plastic component.

Examples of the deterioration preventing agent include various antiaging agents and antioxidants.
Of these, the antioxidant functions to reduce the environmental dependency of the roller resistance value of the conductive roller 4 and to suppress an increase in the roller resistance value during continuous energization. Examples of the antioxidant include nickel diethyldithiocarbamate [NOCRACK (registered trademark) NEC-P manufactured by Ouchi Shinsei Chemical Co., Ltd.], nickel dibutyldithiocarbamate [NOCRACK NBC manufactured by Ouchi Shinsei Chemical Industrial Co., Ltd. ] Etc. are mentioned.

Examples of the filler include one or more of zinc oxide, silica, carbon, carbon black, clay, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, and the like.
By blending the filler, the mechanical strength and the like of the cylindrical foam 1 can be improved.
Moreover, electronic conductivity can also be provided to the cylindrical foam 1 using conductive carbon black as a filler.

The blending ratio of the filler is preferably 5 parts by mass or more, preferably 80 parts by mass or less, particularly 50 parts by mass or less, per 100 parts by mass of the total amount of rubber.
Examples of the scorch inhibitor include one or more of N-cyclohexylthiophthalimide, phthalic anhydride, N-nitrosodiphenylamine, 2,4-diphenyl-4-methyl-1-pentene, and the like. . N-cyclohexylthiophthalimide is particularly preferable.

The blending ratio of the scorch inhibitor is preferably 0.1 parts by mass or more per 100 parts by mass of the total amount of rubber, and is preferably 5 parts by mass or less, particularly preferably 1 part by mass or less.
The co-crosslinking agent refers to a component that itself has a function of crosslinking and also having a function of crosslinking the rubber component to polymerize the whole.
Examples of the co-crosslinking agent include methacrylic acid esters, ethylenically unsaturated monomers represented by metal salts of methacrylic acid or acrylic acid, and polyfunctional polymers using functional groups of 1,2-polybutadiene. 1 type, or 2 or more types, such as dioxime.

Among these, as the ethylenically unsaturated monomer, for example
(a) monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid,
(b) dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid,
(c) an ester or anhydride of the unsaturated carboxylic acid of (a) (b),
(d) the metal salt of (a) to (c),
(e) aliphatic conjugated dienes such as 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene,
(f) aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, ethylvinylbenzene, divinylbenzene,
(g) vinyl compounds having a heterocyclic ring such as triallyl isocyanurate, triallyl cyanurate, vinylpyridine,
(h) In addition, one or more kinds of vinyl cyanide compounds such as (meth) acrylonitrile or α-chloroacrylonitrile, acrolein, formylsterol, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone and the like can be mentioned.

Further, the ester of the unsaturated carboxylic acid (c) is preferably an ester of a monocarboxylic acid.
Examples of the esters of the monocarboxylic acids include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl ( (Meth) acrylate, n-pentyl (meth) acrylate, i-pentyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (Meth) acrylate, i-nonyl (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate ( Alkyl esters of (meth) acrylic acid;
Aminoalkyl esters of (meth) acrylic acid such as aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, butylaminoethyl (meth) acrylate;
(Meth) acrylates having an aromatic ring such as benzyl (meth) acrylate, benzoyl (meth) acrylate, allyl (meth) acrylate;
(Meth) acrylates having an epoxy group such as glycidyl (meth) acrylate, metaglycidyl (meth) acrylate, and epoxycyclohexyl (meth) acrylate;
(Meth) acrylates having various functional groups such as N-methylol (meth) acrylamide, γ- (meth) acryloxypropyltrimethoxysilane, tetrahydrofurfuryl methacrylate;
Polyfunctional (meth) acrylates such as ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene dimethacrylate (EDMA), polyethylene glycol dimethacrylate, isobutylene ethylene dimethacrylate;
1 type, or 2 or more types, etc. are mentioned.

The rubber composition containing each of the above components can be prepared in the same manner as before. First, the rubber component is blended at a predetermined ratio and kneaded, and then the additives other than the foaming agent component and the crosslinking agent component are added and kneaded, and finally the foaming agent component and the crosslinking agent component are added and kneaded. A rubber composition is obtained. For the kneading, for example, a kneader, a Banbury mixer, an extruder or the like can be used.
<Image forming apparatus>
The image forming apparatus of the present invention is characterized by incorporating the conductive roller 4 of the present invention. Examples of the image forming apparatus of the present invention include various image forming apparatuses using electrophotography such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine, or a complex machine of these.

<Example 1>
(Preparation of rubber composition)
As rubber, NBR [JSR N250SL manufactured by JSR Corporation, low nitrile NBR, acrylonitrile content: 20%] 80 parts by mass, EPDM [Esprene (registered trademark) EPDM505A manufactured by Sumitomo Chemical Co., Ltd.] 10 parts by mass, and 10 parts by mass of ECO [HYDRIN (registered trademark) T3108 manufactured by Nippon Zeon Co., Ltd.] was blended.

  And each component shown in following Table 1 was mix | blended with 100 mass parts of said rubber | gum parts, and it knead | mixed for 3 to 5 minutes at 80 degreeC using the closed kneading machine, and prepared the rubber composition.

Each component in Table 1 is as follows. In addition, the mass part in a table | surface is the quantity per 100 mass parts of total amounts of rubber | gum.
Filler: Carbon black HAF [trade name Seast 3 manufactured by Tokai Carbon Co., Ltd.]
Foaming agent: ADCA-based foaming agent (trade name Binhore AC # 3 manufactured by Eiwa Chemical Industry Co., Ltd.)
Foaming aid: Urea-based foaming aid [trade name cell paste 101 manufactured by Eiwa Kasei Kogyo Co., Ltd.]
Acid acceptor: Hydrotalcite [DHT-4A-2 manufactured by Kyowa Chemical Industry Co., Ltd.]
Cross-linking agent: Powdered sulfur [manufactured by Tsurumi Chemical Co., Ltd.]
Accelerator DM: Di-2-benzothiazyl disulfide [Noxer (registered trademark) DM manufactured by Ouchi Shinsei Chemical Co., Ltd.]
Accelerator TS: Tetramethylthiuram disulfide [Noxeller TS manufactured by Ouchi Shinsei Chemical Co., Ltd.]
Acceleration aid: Zinc oxide [manufactured by Hakusuitec Co., Ltd.]
(Formation of cylindrical foam 1)
The rubber composition was supplied to an extruder and extruded through a head cap into an elongated cylinder having an outer diameter of 10.5 mm and an inner diameter of 3.5 mm.

  In addition, the head pressure at the time of extruding a rubber composition was set to 24.5 MPa by setting each part of the extruder to the temperature shown in Table 2 below.

Next, the extruded cylindrical body was cut into a length of 250 mm, heated to 160 ° C. in a vulcanizing can, foamed, and crosslinked for 30 minutes to form a cylindrical foam 1.
(Manufacture of conductive roller 4)
The cylindrical foam 1 is cut into a length of 220 mm, and a metal core (SUM-24L) having an outer diameter of φ6 mm is press-fitted into a through hole 2 at the center thereof, thereby the cylindrical foam 1 After the metal core 3 was electrically joined and mechanically fixed, it was subjected to secondary crosslinking by heating in a hot air oven at 160 ° C. for 60 minutes.

Next, the cylindrical foaming machine is used to traverse the outer surface 5 of the tubular foam 1 so that the radial polishing thickness is 2.8 mm, and both ends of the tubular foam 1 are cut to be conductive. Sex roller 4 was manufactured.
<Example 2>
By setting each part of the extruder to the temperature shown in Table 3 below, the cylindrical foam 1 was formed in the same manner as in Example 1 except that the head pressure during extrusion molding of the rubber composition was set to 19.5 MPa. The conductive roller 4 was manufactured.

<Comparative example 1>
By setting each part of the extruder to the temperature shown in Table 4 below, the cylindrical foam 1 was formed in the same manner as in Example 1 except that the head pressure during extrusion molding of the rubber composition was set to 29.0 MPa. The conductive roller 4 was manufactured.

<Example 3>
The rubber composition was the same as in Example 1 except that 40 parts by mass of SBR [JSR 1502 manufactured by JSR Corporation] was further added to 40 parts by mass of NBR, 10 parts by mass of EPDM, and 10 parts by mass of ECO as a rubber component. Was prepared, the cylindrical foam 1 was formed, and the conductive roller 4 was manufactured.

Although the temperature of each part of the extruder was set to be the same as in Example 1, the head pressure when extruding the rubber composition was 23.9 MPa due to the difference in the combination of rubber components.
<Comparative example 2>
By setting each part of the extruder to the temperature shown in Table 4 above, the cylindrical foam 1 was obtained in the same manner as in Example 3 except that the head pressure when extruding the rubber composition was set to 32.0 MPa. The conductive roller 4 was manufactured.

<Example 4>
As a rubber component, a rubber composition was prepared in the same manner as in Example 1 except that 80 parts by mass of SBR [JSR 1502 manufactured by JSR Co., Ltd.] was blended instead of the NBR, and the cylindrical foam 1 was obtained. The conductive roller 4 was manufactured.
Although the temperature of each part of the extruder was set to be the same as in Example 1, the head pressure when extruding the rubber composition was 24.0 MPa due to the difference in the combination of rubber components.

<Comparative Example 3>
By setting each part of the extruder to the temperature shown in Table 4 above, the cylindrical foam 1 was obtained in the same manner as in Example 4 except that the head pressure when extruding the rubber composition was set to 32.0 MPa. The conductive roller 4 was manufactured.
<Measurement of foam cell diameter>
The conductive roller 4 manufactured in the example and the comparative example is cut in the direction orthogonal to the axial direction, and as shown in FIG. 2, the foam cell in the position closest to the outer surface 5 in the cylindrical foam 1. The foam cell diameter A and the foam cell diameter B of the foam cell closest to the cored bar 3 were measured.

The measurement was performed at three positions in the axial direction of the conductive roller 4 for each of the ten foam cells closest to the outer surface 5 and for each of the ten foam cells closest to the cored bar 3. Values were obtained and used as foam cell diameters A and B.
And ratio B / A of the said foam cell diameter A and B was calculated | required. The larger the ratio B / A is, the smaller the foam cell diameter of the foam cells in the vicinity of the outer surface 5 is, so that the contact area of the outer surface 5 with the surface of the photoreceptor greatly deviates from a predetermined value set in advance. In contrast, the closer to 1, the smaller the foam cell diameter in the vicinity of the outer surface 5 is suppressed, and the displacement of the contact area is suppressed, so that the image defect is less likely to occur. .

  The results are shown in Tables 5 and 6.

  From the results of Examples 1 to 4 and Comparative Examples 1 to 3 in Table 5 and Table 6, in various rubber compositions having different combinations of rubber components, the foaming cell diameter is adjusted by setting the head pressure of the extruder to 25 MPa or less. The ratio B / A of the outer peripheral surface of the cylindrical foam 1 is suppressed to be close to 1 and the foam cell diameter in the vicinity of the outer surface 5 of the cylindrical foam 1 is suppressed, and the contact area of the outer surface 5 with respect to the surface of the photoreceptor is set in advance. It has been found that it is possible to prevent the image from being largely deviated from the predetermined value and to hardly cause the image defect.

  From the results of Examples 1 to 4, it was found that the head pressure of the extruder is preferably 20 MPa or less even in the above range in consideration of further improving the above effects.

DESCRIPTION OF SYMBOLS 1 Cylindrical foam 2 Through-hole 3 Core metal 4 Conductive roller 5 Outer surface

Claims (7)

  A rubber composition having electrical conductivity, crosslinkability, and foamability is continuously extruded into a cylindrical shape through a head of an extruder under a head pressure of 25 MPa or less, and then cut into a predetermined length and vulcanized. A method for producing a conductive roller, comprising a step of forming a cylindrical foam by heating and foaming in a can and crosslinking.   The method for producing a conductive roller according to claim 1, wherein a head pressure during the extrusion is 20 MPa or less.   The manufacturing method of the electroconductive roller of Claim 1 or 2 including the process of grind | polishing the outer surface of the said cylindrical foam.   The method for manufacturing a conductive roller according to claim 3, wherein the outer surface has a radial polishing thickness of 3 mm or less.   The rubber composition includes at least a rubber component, a crosslinking agent component for crosslinking the rubber component, and a foaming agent component, and the foaming agent component is 1 part by mass or more per 100 parts by mass of the total rubber component, 5. The composition according to claim 1, comprising only 10 parts by mass or less of a foaming agent, or comprising the amount of foaming agent and 5 parts by mass or less of a foaming aid per 100 parts by mass of the total rubber content. A method for producing a conductive roller according to claim 1.   A conductive roller manufactured by the manufacturing method according to claim 1.   An image forming apparatus comprising the conductive roller according to claim 6.

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